The proposed project is for the study of hemostatic mechanisms and their relationship to other defenses of the body. In the coming year, continued emphasis will be placed upon surfaced-mediated reactions encompassing the interactions among Hageman factor, plasma prekallikrein, high molecular weight kininogen, plasma thromboplastin antecedent and plasminogen. Studies of the nature of antihemophilic factor will be continued with emphasis on improvement in the method of measuring precipitating antigens.